In a catalyst carrying precious metal particles as the catalyst component on a carrier, to improve the activity, the precious metal particles are carried on the carrier in the form of fine particles. This is so as to make the specific area of the catalyst component as large as possible. However, if reducing the particle size of the catalyst component, the surface energy increases and therefore sintering easily occurs. In particular, in an exhaust gas purification catalyst, the heat of the exhaust gas and the heat of reaction expose the catalyst to a high temperature of several hundred degrees, so the precious metal particles tend to progressively sinter and the particle size to increase and activity to drop.
A catalyst carrier able to prevent sintering of the precious metal catalyst particles is described in Japanese Patent Publication (A) No. 4-180835 and Japanese Patent Publication (A) No. 2002-346387.
Japanese Patent Publication (A) No. 4-180835 discloses an exhaust gas purification catalyst making high activity ceria powder carry a platinum family catalyst metal as large particles of colloid particles. Japanese Patent Publication (A) No. 4-180835 states that according to this exhaust gas purification catalyst, it is possible to prevent sintering of the catalyst metal and entry into solid solution with the ceria powder.
Japanese Patent Publication (A) No. 2002-346387 discloses an exhaust gas purification catalyst arranging an intermediate layer on a carrier and making this intermediate layer carry a nitrogen oxide-removing catalyst comprised of a composite of perovskite-type composite oxide particles and platinum or other precious metal particles. Here, this intermediate layer is formed from a material having affinity with both the nitrogen oxide-removing catalyst and carrier and not causing the nitrogen oxide-removing catalyst component to change much, for example, zirconia, ceria oxide, barium oxide, titania, or a rare earth oxide. Japanese Patent Publication (A) No. 2002-346387 states that this intermediate layer can prevent sintering of the nitrogen oxide-removing catalyst and keep the nitrogen oxide-removing catalyst from reacting with the carrier and being changed.
Further, Japanese Patent Publication (A) No. 9-141098, Japanese Patent Publication (A) No. 4-284847, and Japanese Patent Publication (A) No. 2001-314763 disclose to improve the heat resistance of a catalyst using a zirconia-based catalyst carrier by adding to the zirconia an alkali earth metal, a rare earth, or other stabilization element so as to improve the zirconia's BET ratio surface area, heat stability, etc.